At the present time most TV telemetry signals are transmitted in the clear over conventional analog TV channels. However, because more and more the transmission of TV signals involves the sending of corporate proprietary information, paid television programs and the like, there is a developing demand for encrypted transmission. It is well understood that encryption of analog signals is not satisfactory and accordingly attention has been directed to transmitting encrypted digital signals. Encryption requires the use of an encoder at the transmitter to convert the input video to a digital format and a decoder at the receiver to convert the received digital signals back to the analog TV format. The bit rate at the output of an encoder varies depending upon the application and can be anywhere in the range of from 5 to 40 mbps. At the present state of the art, encryption would limit the upper transmission rate to 10 mbps, however encoded signals per se can be sent at 40 mbps. The present system is directed to formatting the video into digital signals for optimizing the resolution of the output picture. Encryption may be added to the encoded signal train if desired.
If the TV input signal were to be encoded using conventional PCM, the transmitted bit rate would be in the range of 60 to 80 mbps. To achieve the permissible transmission bit rates (5 to 40 mbps), data compression techniques must be employed which reduce the redundancy inherent in the input picture. The objective of the present system is to compress and expand the TV signal within the required bit rate while maximizing the quality of the output picture.